1. Field of the Invention
Exemplary aspects of the present invention generally relate to a lubricant applicator, a process cartridge including the lubricant applicator, and an image forming apparatus including same.
2. Description of the Background Art
With image forming apparatuses such as copiers, printers, facsimile machines and the like, there is increasing market demand for high-quality imaging. In particular, in order to obtain high-resolution color images, efforts to reduce a diameter of particles of toner used to form images and make the toner particles more spherical are being pursued.
Toner particles of substantially small diameter enhance the resolution of the image. At the same time, conglobation of the toner particles improves developability and transferability. One problem, however, is that it is difficult to produce small-diameter spherical toner particles with a known kneading pulverization method. Thus, polymerized toner manufactured by toner manufacturing methods such as a suspension polymerization method, an emulsion polymerization method, and a dispersion polymerization method began to be used.
Although advantageous, such small-diameter spherical toner has a drawback in that it complicates cleaning of a photoreceptor after an image forming operation, as the following discussion explains.
One known method of removing the toner from the photoreceptor and thus cleaning the photoreceptor involves use of a cleaning blade. However, use of small-diameter spherical toner makes it difficult to remove the toner with the cleaning blade because the cleaning blade removes the toner and the like while slidably contacting the surface of the photoreceptor. This sliding contact or scraping action causes deformation of an edge portion of the cleaning blade due to friction resistance with the photoreceptor, and can result in breaking the contact between the blade and the photoreceptor, thereby undesirably forming a gap between the photoreceptor and the cleaning blade. As a result, a certain amount of the toner slips through the gap between the photoreceptor and the cleaning blade. If the amount of toner slips from the cleaning blade is large enough, it can cause abnormal imaging including fogging, etc.
Furthermore, when the toner slips past the cleaning blade, the toner keeps accumulating on the surface of the photoreceptor, and a release agent and a fluidizing agent in the toner adhere to the surface of the photoreceptor in the form of a membrane or film. This phenomenon is known as filming. When such filming occurs, an abnormal image is formed, in which, for example, a solid portion of an image may include white spots.
To counteract such problems, a method for reducing a friction coefficient of the surface of the photoreceptor has been proposed to improve cleaning performance of the cleaning blade relative to the surface of the photoreceptor.
In this related-art method, a thin film is formed on the photoreceptor by applying a lubricant formed of metal salts of fatty acids or the like to the surface of the photoreceptor to reduce the friction coefficient of the surface of the photoreceptor is reduced. When the friction coefficient of the surface of the photoreceptor is reduced, adhesion between the photoreceptor and the toner is reduced, thereby improving the cleaning performance of the cleaning blade while suppressing filming.
Typically, a lubricant applicator in the form of a brush or the like is used to apply the lubricant to the photoreceptor. However, in a case in which an image having a relatively high image area ratio is printed continuously, when a large amount of toner adheres to the lubricant application brush, the lubricant sticks to the toner on the brush, thereby preventing the lubricant from being supplied to the surface of the photoreceptor even if the lubricant application brush frictionally contacts the lubricant. Thus, it is advantageous to minimize the amount of toner adhered to the surface of the lubricant application brush when the lubricant application brush scrapes the lubricant.
In view of the above, one related-art approach disposes the lubricant applicator downstream of the cleaning blade. With this configuration, the cleaning blade cleans residual toner remaining on the photoreceptor after a transfer process so that the lubricant can be applied to the surface of the photoreceptor without being affected by previous imaging. However, in order to apply the lubricant, a smoothing member is necessary, thereby complicating efforts to reduce the size and the cost of the image forming apparatus.
By contrast, in another related-art approach, the lubricant applicator such as an application brush is provided upstream of the cleaning blade and applies a solid lubricant to the photoreceptor. However, with this configuration the toner remains on the application brush, preventing the lubricant from being applied effectively to the photoreceptor.
In still another related-art approach, a lubricant applicator or application roller such as a brush roller or a sponge roller applies a lubricant formed generally of zinc stearate to the photoreceptor serving as an image bearing member and to an intermediate transfer belt in an effort to improve overall transferability including cleaning performance, extend product life of the photoreceptor and the intermediate transfer belt, and prevent image transfer failure.
In particular, the application roller is rotatably provided on an image bearing surface of the image bearing member such that the peripheral surface of the image bearing member evenly contacts the application roller. The application roller rotates together with rotation of the image bearing member. Alternatively, when the application roller rotates, the lubricant contacts the application roller at a predetermined pressure. In this case, the lubricant is pressed against the application roller by its own weight or by a spring force of a spring, thereby securing a predetermined contact pressure in order to acquire the lubricant and apply it to the surface of the photoreceptor.
However, when a solid lubricant is pressed against the application roller, the lubricant is turned into a powder. Then, the application roller contacting the image bearing member applies a powdered lubricant to the image bearing member. Moreover, the solid lubricant is urged by its own weight or by the spring to secure the predetermined pressure. Thus, the lubricant is always supplied in powder form to the image bearing member. Accordingly, regardless of the state of the image bearing member, a certain amount of the powder lubricant is always supplied. Consequently, depending on the state of the image bearing member, some of the powder lubricant scraped off from the solid lubricant may not be applied to the image bearing member but instead accumulates in a cleaning unit, on the cleaning blade or in the application roller in the cleaning unit. As a result, upon maintenance, such powder lubricant scatters and falls off. When the powder lubricant accumulates on the cleaning blade, the accumulated lubricant presses the cleaning blade. Depending on the amount of accumulation, the amount of pressure of the cleaning blade pressing the image bearing member changes undesirably, causing degradation of cleaning performance.
In one example of removing the toner adhered to the lubricant application brush, a flicker member is employed to remove toner from the brush. However, the flicker member is insufficient because, after the toner is removed from the brush by flicking, the toner sticks again to the brush due to airflow.
In order to facilitate an understanding of the related art and of the novel features of the present invention, with reference to FIGS. 3 and 4, a function of a flicker member of a related-art lubricant applicator is described. FIG. 3 is a partially enlarged view of the related-art lubricant applicator. FIG. 4 is a diagram conceptually illustrating the function of the flicker of the related-art lubricant applicator.
In FIGS. 3 and 4, substantially below a brush roller 203a, a flicker 209 is disposed so as to contact the brush roller 203a. The flicker 209 is formed of a stainless steel stick or the like and disposed upstream from a solid lubricant 203b in the direction of rotation of the brush roller 203a. Accordingly, a gap 210 is formed between the flicker 209 and the solid lubricant 203b, allowing toner T removed from the brush roller 203a by the flicker 209 to stick again to the brush roller 203a due to airflow or the like, thus hindering the lubricant from adhering to the brush roller 203a as the solid lubricant 203b and the brush roller 203a slidably contact each other.
In other words, because the brush roller 203a bears the toner T, it is difficult for the brush roller 203a to carry the lubricant in powder form, as indicated by a dotted oval in FIG. 4. As a result, the brush roller 203a cannot adequately supply the lubricant to the surface of the photoreceptor.